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Defending strike
shaman attack 1

Target: one creature

Attack: Wisdom vs. Reflex

Hit: "1d8 + Wisdom modifier damage. Until the end of your next turn, you and your allies gain a +1 power bonus to AC while adjacent to your spirit companion."
Level 21: "2d8 + Wisdom modifier damage."[PH2:121]

Defending strike is an at-will power available to shamans at 1st level.